1.下载composer.phar
wget https://getcomposer.org/composer.phar
2.重命名composer.phar为composer
mv composer.phar composer
3.增加可执行权限
chmod +x composer
4.现在可以通过./composer 命令运行composer，但这只仅限于在当前目录运行。要想全局使用，composer ，要设置把它为全局变量。找到composer文件，把它移到/usl/local/bin 目录，这样就可以在全局使用composer 命令。
sudo mv composer /usr/local/bin
5.测试
jiqing@ubuntu:/opt$ composer
______
/ ____/___ ____ ___ ____ ____ ________ _____
/ / / __ / __ `__ / __ / __ / ___/ _ / ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__ ) __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
/_/
Composer version 1.7-dev (c2fbbe3b86788eb507a0f4f45f9fdc623ca579c4) 2018-03-29 21:36:46
Usage:
command [options] [arguments]
Options:
-h, --help Display this help message
-q, --quiet Do not output any message
-V, --version Display this application version
--ansi Force ANSI output
--no-ansi Disable ANSI output
-n, --no-interaction Do not ask any interactive question
--profile Display timing and memory usage information
--no-plugins Whether to disable plugins.
-d, --working-dir=WORKING-DIR If specified, use the given directory as working directory.
-v|vv|vvv, --verbose Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug
Available commands:
about Shows the short information about Composer.
archive Creates an archive of this composer package.
browse Opens the package's repository URL or homepage in your browser.
check-platform-reqs Check that platform requirements are satisfied.
clear-cache Clears composer's internal package cache.
clearcache Clears composer's internal package cache.
config Sets config options.
create-project Creates new project from a package into given directory.
depends Shows which packages cause the given package to be installed.
diagnose Diagnoses the system to identify common errors.
dump-autoload Dumps the autoloader.
dumpautoload Dumps the autoloader.
exec Executes a vendored binary/script.
global Allows running commands in the global composer dir ($COMPOSER_HOME).
help Displays help for a command
home Opens the package's repository URL or homepage in your browser.
info Shows information about packages.
init Creates a basic composer.json file in current directory.
install Installs the project dependencies from the composer.lock file if present, or falls back on the composer.json.
licenses Shows information about licenses of dependencies.
list Lists commands
outdated Shows a list of installed packages that have updates available, including their latest version.
prohibits Shows which packages prevent the given package from being installed.
remove Removes a package from the require or require-dev.
require Adds required packages to your composer.json and installs them.
run-script Runs the scripts defined in composer.json.
search Searches for packages.
self-update Updates composer.phar to the latest version.
selfupdate Updates composer.phar to the latest version.
show Shows information about packages.
status Shows a list of locally modified packages.
suggests Shows package suggestions.
update Upgrades your dependencies to the latest version according to composer.json, and updates the composer.lock file.
upgrade Upgrades your dependencies to the latest version according to composer.json, and updates the composer.lock file.
validate Validates a composer.json and composer.lock.
why Shows which packages cause the given package to be installed.
why-not Shows which packages prevent the given package from being installed.
引入一个类库，并使用。
sudo composer require aferrandini/phpqrcode
使用的时候，很简单，只要引入一下自动加载就可以了。
require '../vendor/autoload.php';
PHPQRCodeQRcode::png("Test", "../tmp/qrcode.png", 'L', 4, 2);
如果是tp等框架，可以将引入部分放在index.php的入口文件，这样每个地方都可以灵活使用插件了。